1. Field of the Invention
The invention relates to a susceptor, in particular, a susceptor in which a SiC film formed on a wafer pocket is partially left without polishing so as to be a SiC grain growth surface portion.
2. Description of the Background Art
A semiconductor device is manufactured through many manufacturing processes. As susceptors that are used in an epitaxial growth process of a semiconductor wafer, because of the low reactivity and high strength, a SiC member in which SiC is coated on a carbon base material is frequently used.
There are a sheet-like susceptor in which a single wafer-housing recess is formed on a planar susceptor base material and a susceptor in which many recesses are formed on a planar susceptor base material.
The susceptor is manufactured by coating SiC on a carbon base material in which a recess is formed by means of the mechanical grinding or the like, followed by using as coated in the heat treatment or the like (refer to Japanese Patent Unexamined Publication No. JP-A-56-10921), or by further polishing the SiC coated surface by use of a polishing machine, followed by using in the heat treatment or the like (refer to Japanese Patent Unexamined Publication No. JP-A-7-335572).
However, in the susceptors manufactured according to the conventional manufacturing methods, when the susceptor is used as coated with a SiC film in the heat treatment like in the JP-A-56-10921, because SiC is very hard, when grains grow large, apexes of the grains work like a blade to cut a surface of a semiconductor wafer. Furthermore, when the coated surface is polished and used as shown in the JP-A-7-335572, stress is concentrated during the polishing process in the vicinity of a boundary portion between a bottom surface portion of the recess where a semiconductor wafer is mounted on and a vertical portion thereof to cause fine cracks in the film. Furthermore, in some cases, owing to the thermal stress during the heat treatment, with the fine crack as a starting point, cracks as shown in FIG. 6 are generated on the coated surface, resulting in a short lifetime.
Furthermore, when an entire surface of the recess where a wafer is placed is polished, in the recess, the wafer, owing to a gas remaining at a contact interface, is easy in sliding, and the gas tends to linger at a peripheral corner portion of the recess. Accordingly, there is a problem in that owing to a centrifugal force in association with a rotary motion of the susceptor and an influence of the gas, the wafer comes off the recess.
In order to overcome the problems, countermeasures such as disposing holes communicating to a susceptor bottom surface on a wafer contact surface of the recess or disposing grooves in lattice are adopted. However, in this case, there is a problem in that since a partial temperature difference is formed in the wafer surface, the wafer cannot be performed uniformly heat treatment.
Furthermore, in the conventional susceptors, an outer circumference planar portion continuing from the outer circumference portion of the recess where the wafer is placed is subjected to an ordinary CVD-SiC coating or to the mirror polishing. In the former one, a gas flow is disturbed at the outer circumference portion of a wafer mounting portion to deteriorate, for instance, the uniformity of a wafer epitaxial layer. Furthermore, when it is used repeatedly, in the outer circumference portion, it is highly likely that impurity components agglomerate to adversely affect on the wafer. In the latter case, since the gas flow in the outer circumference portion becomes excessively uniform to cause an abnormal growth protrusion in a deposition layer, for instance, on a downstream side of the gas, after the repetition use, the uniformity of the epitaxial layer of the wafer may be deteriorated.